Vol. 13, No. 4, 2020

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On equidistant polytopes in the Euclidean space

Csaba Vincze, Márk Oláh and Letícia Lengyel

Vol. 13 (2020), No. 4, 577–595

An equidistant polytope is a special equidistant set in the space n all of whose boundary points have equal distances from two finite systems of points. Since one of the finite systems of the given points is required to be in the interior of the convex hull of the other one, we can speak about inner and outer focal points of the equidistant polytope. It is of type (q,p), where q is the number of the outer focal points and p is the number of the inner focal points. The equidistancy is the generalization of convexity because a convex polytope can be given as an equidistant polytope of type (q,1), where q n + 1. We present some general results about the basic properties of the equidistant polytopes: convex components, graph representations, connectedness, correspondence to the Voronoi decomposition of the space etc. In particular, we are interested in equidistant polytopes of dimension 2 (equidistant polygons). Equidistant polygons of type (3,2) will be characterized in terms of a constructive (ruler-and-compass) process to recognize them. In general they are pentagons with exactly two concave angles such that the vertices at which the concave angles appear are joined by an inner diagonal related to the adjacent sides of the polygon in a special way via the three reflections theorem for concurrent lines. The last section is devoted to some special arrangements of the focal points to get the concave quadrangles as equidistant polygons of type (3,2).

Euclidean geometry, convex geometry, equidistant sets
Mathematical Subject Classification 2010
Primary: 51M04
Received: 2 September 2019
Revised: 20 July 2020
Accepted: 21 July 2020
Published: 20 November 2020

Communicated by Michael Dorff
Csaba Vincze
Institute of Mathematics
University of Debrecen
Márk Oláh
Institute of Mathematics
Doctoral School of Mathematical and Computational Sciences
University of Debrecen
Letícia Lengyel
Mathematics MSc
Institute of Mathematics
University of Debrecen